1. Field of the Invention
This invention relates to a liquid crystal display (LCD) panel, and more particularly to a LCD panel having a planar insulating layer, a counter electrode and a pixel electrode, wherein both electrodes are made of a transparent conductive material, such that the aperture ratio of the LCD panel may be efficiently increased, and that the interaction between the electrodes may be decreased.
2. Description of the Prior Art
Liquid crystal molecules in a liquid crystal display (LCD) device have optical anisotropy and chiral properties. The liquid crystal molecules have an orientation order in alignment resulting from their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field there to. In other words, as the electric field is changed, the alignment direction of the liquid crystal molecular is changed. The incident light is refracted to the alignment direction of the liquid crystal molecular owing to the optical anisotropy of the liquid crystal molecules. Therefore, the LCD device can display an image by means of two polarizers and the liquid crystal molecules.
In most of the conventional LCD devices, the alignment of the liquid crystal is controlled by applying a vertical electric field. Such mechanism has the advantages of high transmittance and high aperture ratio. However, the disadvantage of such an LCD lies in a narrow viewing angle. To overcome the problem of the narrow viewing angle, an in-plane switching (IPS) LCD panel has been developed. In the IPS LCD panel, the alignment of liquid crystal is controlled by an electric field parallel to the LCD panel. Such mechanism is different from the LCD panel mentioned above as the Twisted Nematic (TN) or Super Twisted Nematic (STN) LCD panel. The electric field applied to the IPS LCD device is lateral because the pixel and common electrodes thereof are formed on the same substrate in the IPS LCD device. The advantages of the IPS LCD device lie in a wide viewing angle and low color dispersion.
The IPS LCD device usually comprises separate and parallel upper and lower substrates and liquid crystal molecules positioned in between. On the lower substrate or array substrate, a pixel electrode and a common electrode are formed, separately and parallel to each other. The alignment of the liquid crystal is changed by the lateral electric field generated between the pixel and common electrodes. However, the conventional IPS LCD device uses opaque metal as the pixel and counter electrode material, as disclosed in US Publication No. 2002-0158994. The US Publication No. 2002-0158994 discloses a manufacturing method of liquid crystal display device, and one pixel portion of the LCD device is shown in FIG. 1. The pixel portion comprises a drain line A, a drain electrode H, a gate line M, a common electrode B, a pixel electrode (drain layer) F, counter electrode (indium tin oxide, ITO) C, a pixel electrode (ITO) D, a source electrode K, and a thin film transistor (TFT) positioned near the intersection portion among the source electrode K, the drain electrode H, and a semiconductor layer L. Therein, the pixel portion further comprises a contact hole G for the pixel electrode F, and a contact hole J for the counter electrode C. Although the LCD device could provide a wide viewing angle, simplified process and high reliability, the pixel electrode F in the pixel is made of opaque conductive metal, which may result in a low aperture ratio and may affect the brightness of the LCD device.
Accordingly, an IPS LCD device still needs to be improved in its aperture ratio and brightness.